1. Field of the Invention
The present disclosure relates to liquid crystal display technology, and more particularly to a driving circuit of liquid crystal panels and the driving method thereof.
2. Discussion of the Related Art
A driving circuit having a resolution of 720*1280 of liquid crystal panels is shown as in FIG. 1 as an example. The driving circuit 10 includes a plurality of scanning lines (X) arranged along a row direction, and the scanning lines (X) are parallel to each other. In FIG. 1, there are 2160 scanning lines (X). The driving circuit 10 also includes a plurality of data lines (Y) parallel to each other. In FIG. 1, there are 3840 columns. The data line (Xm) and the scanning line (Ym) intersect with each other, wherein m is a positive integer in a range between 1 and 2160, and n is a positive integer in a range between 1 and 3840. A plurality of subpixels 110 are arranged at the intersections of the scanning lines (X) and the data lines (Y). Specifically, each of the subpixels 110 includes a field effect tube (FET) (T) and a capacitor unit (A), which is also known as pixel electrode. The FET (T) includes a gate (G), a source (S), and a drain (D). The capacitor (A) includes liquid crystal capacitor (Clc) and a storage capacitor (Cs). One end of the storage capacitor (Cs) connects to the drain (D) and the source (S). As shown in FIG. 1, one end of the storage capacitor (Cs) connects to the drain (D), and the other end of the storage capacitor (Cs) connects to the common voltage (Vcom). The gate (G) of the FET (T) of the subpixels 110 in the same row connects to the corresponding scanning line (X). Similarly, the source (S) of the FET (T) of the subpixels 110 in the same column connect to the corresponding data line (Y). In this way, the gate (G) of the subpixels 110 may be turned on or off by configuring the scanning voltage (VGm) of the scanning line (Xm) to be high or low. When the VGm is turned on, the data voltage (VSn) of the data line (Y) of the subpixels 110 in the column may be received such that the drain (D) or the capacitor unit (A) may be charged and the data voltage corresponding to the grayscale may be received. In this way, the subpixels 110 displays images corresponding to the grayscale when being driven by the voltage of the scanning line (X) and the data line (Y). The scanning lines (X) are turned on in sequence, and the data voltage for displaying the grayscale is written via the data line (Y) such that the images may be displayed normally.
In order to avoid the direct-current blocking effect and the direct-current residual effect of the liquid crystal panels, an alternating current (AC) voltage has to be applied to two ends of the liquid crystal. The common electrode (Vcom) is the reference voltage of the AC voltage. That is, the data voltage (VSn) owns a positive polarity and a negative polarity. In FIG. 1, VDDA owns positive polarity when comparing to the Vcom, and VSSA owns the negative polarity when comparing to the Vcom. Thus, during the driving operations of the liquid crystal panel, the drain voltage (VD), which is also called as pixel voltage, is charged from a positive polarity to a negative polarity and then from the negative polarity to the positive polarity by the data voltage of the data line (Y). Thus, the charging process has to be completed during the turn-on time period of the FET (T) of each of the scanning line (Xm). In order to achieve this object, during the pre-charge operations, the data voltage (VSn) of the previous row having the same polarity has to be applied to the current row, and thus the polarity of the drain voltage (VD) of the subpixels 110 of the current row is inversed, which ensures the liquid crystal capacitor (Clc) can quickly achieve the voltage level corresponding to the grayscale needed. In addition, due to the increasing resolution and the refresh rate of the liquid crystal panel, the turn-on time period for each of the scanning line (Xm) is greatly reduced, which results in insufficient charging time period.
FIGS. 2, 3, 4a, and 4b relate to the conventional driving method having the same predetermined pre-charge time period. FIG. 2 is a schematic view of the pre-charge scanning voltage waveforms for dot inversion and column inversion of FIG. 1, wherein CKV represents the clock pulse control signals and Gm represents the pre-charge scanning voltage waveform corresponding to the scanning line (Xm). Gm may also be called as row-scanning-driving voltage signals, and may be converted into row scanning voltage (VGm). Before the data voltage (VSn) for displaying corresponding grayscale is inputted to the data line (Y), the scanning line (X) is turned on to apply the pre-charge operations to the subpixels 110 to be displayed. For instance, during the time period (t2), the voltage waveforms corresponding to G1 and G2 turn on the subpixels 110 corresponding to the scanning lines (X1, X2). At this moment, as shown in FIG. 4b, the data voltage (V2) corresponding to the subpixels 110(1,1) is inputted to the data line (Y1) of the subpixels 110(2,1) in the same column and in the next row. This operation pre-charge the subpixels 110(2,1) in the X2 row, and the polarity of the data voltage (V1), as shown in FIG. 4a, is charged by the data voltage (V2) corresponding to the subpixels 110(1,1) and then is inversed. During the time period (t3), the data voltage (V3) needed for displaying the corresponding grayscale of the subpixels 110(2,1) is written. FIG. 3 is an example, wherein V2>V3>V1. This method intends to reduce the charging time period needed for inversing the negative polarity of the previous frame to the positive polarity, wherein the polarity of V3 is positive in view of Vcom. However, as the pre-charge time period (t2) is a fixed value, such as a clock period (CKV) shown in FIG. 2, the subpixels 110(2,1) may reach the data voltage level of V2 during the time period (t2). When writing the data voltage (V3) corresponding to the needed grayscale, the V2 drops to be V3, which extends the pre-charge time period to be t4. This has not achieved the object of reducing the charging time period. On the contrary, the pre-charge time period is increased.
Such pre-charge method pre-charges the subpixels 110 on each of the scanning lines (X), and the pre-charge time period are the same. That is, t1=t2=t3=. . . tm. As the data voltage corresponding to the subpixels 110 in the previous row is charged to the subpixels 110 in the current row and in the same column, some of the frames that are not needed to be pre-charged may be turned on or the pre-charge time period for some of the frames is too long, which results in higher power consumption and higher temperate of the driving circuit. At the same time, as the scanning line (X) is turned on in advance, the abnormal data voltage may be written into the liquid crystal panel, which results in a bad sharpness of the display images.
In view of the above, conventional technology cannot satisfy the demands toward low power consumption and high sharpness of the liquid crystal panels.